Despite rapid advances in surgical interventions, prolonged immobilization still forms an integral part of many therapeutic interventions. The purpose of this study was to quantify the metabolic, morphological and functional changes in skeletal muscle as a result of surgery and long-term immobilization. 31P-MRS, MRI, biodex and biopsy measurements were performed on 12 healthy subjects and 6 patients with an ankle fracture treated surgically followed by 8 weeks of cast immobilization (IM). All measurements were performed 1 week after casting was discontinued. Four of the patients were studied longitudinally and measurements were made during (MRI) at 5 and 10 weeks after removal of the cast (post-IM). Eight weeks of IM resulted in significant morphological, functional and metabolic alterations of skeletal muscle. Volumetric data revealed that atrophy did not occur uniformly along the length of the muscle but was localized within the muscle belly. Muscle strength was decreased by 45.9-52.8% at all angular velocities. In contrast, relative fatigue during exercise was less in the involved leg (30.7 +8.5%) than the control leg (52.1+8.3%) and could not be accounted for by decreased muscle mass or central fatigue. IM was also associated with a shift in the metabolic profile. One week post-IM, the basal Pi content was elevated. Furthermore, the oxidative and glycogenolytic properties of IM muscle were altered. Based on longitudinal studies, metabolic and functional characteristics of IM muscles returned to control values within 10 weeks.